Various approaches are known with regard to controlling the glossiness of images printed using an ink jet printer.
Pin and Cure
A pin and cure system is known that allows adjustment of the gloss level of a printer's output. This helps a print shop tailor its products to its customer's needs. Such system consists of a set of adjustable UV LED pin lamps mounted inline with the printing area, and a set of larger mercury arc lamps after the print area. The adjustable nature of the LED lamps allows the ink to be set in place and the amount of flow to be controlled. Ink that is allowed to flow after being placed develops a smoother, glossier surface. Ink that is pinned harder does not flow and develops a more matte surface.
FIG. 1 is a graph that shows glossiness in gloss units vs. pin lamp levels in mW/cm. This behavior allows the printer operator to select the level of gloss for the printer output. This type of pinning relies heavily on the ink chemistry and its interaction with the substrate. Surface tensions of various media effect the amount of flow and the rate at which curing occurs. This, in turn, means that each media needs a specific configuration because the curve shown in FIG. 1 varies with media.
When the printer operator adjusts the pin and cure settings for various media, the chance of producing an unpredictable output having poor print quality is increased. Also, this process is time consuming as well as tedious. Because of the wide range of materials onto which an ink jet printer can print, it is possible to adjust the system so that the output is not acceptable, i.e. by introducing cure banding, as well as other print artifacts, such as ink bleed
Other Methods
Before pin and cure was available, there were already other methods of controlling the gloss on output from UV printers and other inkjet printers, such as LED printers, etc.
Printers manufactured by EFI, as well as those from other manufacturers, have always had the ability to adjust the UV lamp output. In this category of printer lower lamp output results in glossier prints. The drawback of this type of control is cure quality, adhesion, and surface feel suffer when the ink is not cured sufficiently.
Another method of gloss control involves adjusting the time-to-lamp. In a scanning printer it is usually possible to select a leading-lamp or post cure mode. This provides extra time from when the ink is jetted until it is cured, thus allowing drop spread and increased gloss. A significant problem with this approach is that time-to-lamp is affected by image width. Adding a delay between passes helps with uniformity, but impacts throughput.
Offset and screen printers address the issue of image gloss by allowing the printer operator to choose a gloss, semi-gloss, or matte ink.
Another option the printer operator has is during finishing. Printer output can be post coated or laminated. Some printers also offer a clear varnish internal to the machine. This type of printer is also suited to spot gloss.
Two-Pass Spot-Gloss
Some flat bed printers have a feature in which they offer spot-gloss without a clear ink. Their configurations allow the printer to print the entire image twice. First, the gloss areas are printed with their UV lamps at a low intensity. This allows for ink flow and a gloss surface. Then, the matte areas are printed, where the matte effect is accomplished by higher UV settings and less ink flow. The high cure over the already printed gloss areas insures a quality cure and no adhesion issues. However, a two-pass approach impacts throughput and can result in artifacts due to registration errors that occur as a result of the two-passes.